One or more embodiments of the invention generally relate to radio communication. More particularly, certain embodiments of the invention relates to synchronization.
The following background information may present examples of specific aspects of the prior art (e.g., without limitation, approaches, facts, or common wisdom) that, while expected to be helpful to further educate the reader as to additional aspects of the prior art, is not to be construed as limiting the present invention, or any embodiments thereof, to anything stated or implied therein or inferred thereupon.
The following is an example of a specific aspect in the prior art that, while expected to be helpful to further educate the reader as to additional aspects of the prior art, is not to be construed as limiting the present invention, or any embodiments thereof, to anything stated or implied therein or inferred thereupon. By way of educational background, an aspect of the prior art generally useful to be aware of is that in the field of radio communications and specifically frequency hopping systems typically within shared frequency bands with a multiplicity of uncoordinated devices competing for the same spectrum within the same geographic area, it may commonly be useful to practice interference prediction, mitigation, and avoidance when certain transmission characteristics are known such as the maximum duration a frequency may be transmitted by a given device within a given period of time and whether or not frequencies are used evenly on average over a given period of time. In the frequency hopping radio communications marketplace there is typically a growing demand for devices that can mitigate interference between competing devices on separate networks without the expense or complexity of an added frequency coordination component that must be administrated either in software or by the user themselves. Furthermore, real time data transmission and reception such as digital voice and other data transmission applications over frequency hopping systems within the same network are usually more efficient when synchronization may be fast and delays due to re-sending data are at a minimum.
With most frequency hopping systems using digital modulation techniques, typically as data rates increase the range may be reduced in the form of wider transmit bandwidth causing degraded receiver sensitivity due to widening the receive filter bandwidth, therefore an efficient payload to overhead ratio may be desired to maximize throughput while minimizing receive degradation due to widening the receive filter bandwidth. In mobile data and voice applications receiving devices commonly go in and out of range of the transmitted signal which may commonly cause hopping synchronization loss. Usually the less expensive the clock reference the shorter the duration of signal loss that will be tolerated before re-synchronization is required. Typically in frequency hopping systems that utilize a multitude of frequencies within their hop cycle, one method of synchronizing a frequency hopping receiver with a frequency hopping transmitter without the delays associated with the receiver scanning all frequencies in a particular hopset or waiting on one channel until that channel may be used within the hop cycle, may be for the receiver to tune to or scan one or more of a small number of predesignated channels from the hopset while the transmitter always begins transmission of the hopping cycle starting with that/those same frequencies before proceeding on to the rest of the cycle.
In order to keep frequency usage equally distributed over time the transmit duration of the frequencies used to start synchronization are commonly kept the same as non-synchronization transmissions. Usually this forces receiver scan times thus the delay time to synchronization to be directly proportional to the per frequency transmit duration of the particular frequency hopping system. Furthermore, if the receiver loses synchronization it must commonly wait until the hop cycle cycles back around to those start frequencies described above in order to regain synchronization. Another known solution may be for the receiver to hop at a much slower rate than the transmitter. The receiver hop dwell times will typically be the transmitter dwell time multiplied by the number of channels, however this can lead to significant synchronization delay as the number of designated hopping channels increases in a system. One way to solve the receive scan time issue may be to use multiple scanning receivers each coordinated to tune to different frequencies in order to speed up the scanning and thus the synchronization. This however may be costly and does not help to increase the payload data throughput efficiency on the transmit side.
In view of the foregoing, it is clear that these traditional techniques are not perfect and leave room for more optimal approaches.
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